1. Field of the Invention
The present invention relates to a gas turbine combustor.
2. Related Art
Gas turbine combustors of the prior art will be described with reference to FIGS. 5 and 6.
In a gas turbine combustor of the prior art, as shown in FIGS. 5 and 6, there is arranged at the center of the section of the combustor a pilot fuel nozzle 104 for producing a flame portion. Around this pilot fuel nozzle 104, there is a cylindrical outer cylinder 106, on which there are arranged a plurality of main fuel nozzles 102 for producing a premixed gas of a fuel and air.
The pilot fuel nozzle 104 is provided with a pilot swirler 103. Each of the main fuel nozzles 102 is provided with main swirlers 101 which are arranged around the main fuel nozzle 102 and extend to the outer cylinder 106. A plurality of nozzle ports 105 are opened in the nozzle body wall face of the main fuel nozzle 102 downstream of the main swirlers 101.
In the construction described above, the air and the fuel flow in the directions, as indicated by arrows in FIGS. 5 and 6, so that the air and the fuel are fed from a plurality of main swirlers 101 and one pilot swirler 103, and from a plurality of main fuel nozzles 102 and one pilot fuel nozzle 104, respectively, to the combustion zone.
The fuel thus fed from the main fuel nozzle 102 is injected from the nozzle ports 105 in the nozzle body wall face so that it is mixed with the air flowing through the main swirlers 101 around the nozzle outer circumference to prepare a premixed gas.
In the combustor of the prior art, the main fuel nozzle 102, the main swirlers 101 and the outer cylinder 106 construct a main fuel nozzle device.
The main fuel nozzle device of the gas turbine combustor of the prior is of the type in which the fuel is injected from the nozzle ports formed in the wall face of the nozzle body, as described hereinbefore.
This system has a problem in that the premixture to be prepared in the vicinity of the exits of the main swirlers has a tendency to become a gas having a higher fuel concentration at its center portion. Another problem is that the pressure for feeding the fuel has to be set at a high level for establishing a fuel penetration necessary for mixing the fuel, injected from the main fuel nozzles, efficiently with the air flow.
Another example of the gas turbine combustor of the prior art is shown in FIG. 7.
In a gas turbine combustor 201 of the prior art, as shown in FIG. 7, there is formed a combustion chamber 212 which is enclosed and defined by both an axially symmetrical cylindrical upstream inner cylinder 206 and a downstream inner cylinder 207 connected at its leading end portion to the rear end portion of the upstream inner cylinder 206.
The downstream inner cylinder 207 forming the combustion chamber 212 together with the upstream inner cylinder 206 is composed of a plurality of cylinders, with these cylinders increasing in diameters from the inner cylinder 206 to a downstream-most cylinder. A clearance is formed at the joint between adjacent inner cylinders 207 so that compressed air flowing outside of the upstream inner cylinder 206 and the downstream inner cylinder 207 may flow as cooling air 217 through this clearance into the downstream inner cylinder 207, and then may flow further along the inner circumference of the downstream inner cylinder 207 to cool the downstream inner cylinder 207 from its inside to then protect it from the combustion gas which is at a high temperature and under a high pressure. Air as indicated by arrows 204 and 210 flows respectively through swirlers 203 and 209.
In the gas turbine combustor 201 of the prior art, as has been described hereinbefore, a pilot nozzle 202 and a main nozzle 208 are arranged in the upstream inner cylinder 206 on the upstream side of the combustion chamber 212. A pilot fuel 213 and a main fuel 215, i.e. the fuels necessary for the operation of the gas turbine, are fed to the upstream side of the combustion chamber 212. As a result, the ratio of the unburned fuel to the fed fuel has a high value on the upstream side but gradually lowers toward the downstream side, as plotted in the distribution of the unburned fuel in the axial direction of the combustor in FIG. 8.
Specifically, the ratio of the fuel being burned in a section in the combustion chamber 212, i.e., the so-called "sectional load factor" is high on the upstream side, but a certain unburned fuel ratio is maintained even within a range on the downstream side so that the sectional load factor is shared. As a result, the combustion in the combustion chamber 212 can maintain a stable combustion and a low NOx emission.
Gas turbines have been demanded in recent years to have a high temperature and a high pressure of the combustion gas for a larger size and a higher efficiency. However, the reaction rate of the fuel, as fed to the combustion chamber 212, is increased by the high temperature and pressure of the combustion gas. If 100% of the fuels 213 and 215 required for running the gas turbine are fed on the upstream side, therefore, they are instantly burned on the upstream side, and the unburned gas has a small distribution on the downstream side. As a result, the sectional load factor rises on the upstream side and causes problems of an unstable combustion state and an increase in the NOx emission.